全文获取类型
收费全文 | 80492篇 |
免费 | 7894篇 |
国内免费 | 4576篇 |
专业分类
电工技术 | 6343篇 |
技术理论 | 2篇 |
综合类 | 6010篇 |
化学工业 | 11585篇 |
金属工艺 | 5110篇 |
机械仪表 | 5616篇 |
建筑科学 | 5561篇 |
矿业工程 | 2218篇 |
能源动力 | 2649篇 |
轻工业 | 5430篇 |
水利工程 | 1913篇 |
石油天然气 | 3476篇 |
武器工业 | 1015篇 |
无线电 | 10254篇 |
一般工业技术 | 9052篇 |
冶金工业 | 3949篇 |
原子能技术 | 1062篇 |
自动化技术 | 11717篇 |
出版年
2024年 | 272篇 |
2023年 | 959篇 |
2022年 | 1988篇 |
2021年 | 2956篇 |
2020年 | 2224篇 |
2019年 | 1750篇 |
2018年 | 1988篇 |
2017年 | 2434篇 |
2016年 | 2384篇 |
2015年 | 3169篇 |
2014年 | 4137篇 |
2013年 | 4929篇 |
2012年 | 6158篇 |
2011年 | 6532篇 |
2010年 | 6097篇 |
2009年 | 5889篇 |
2008年 | 5761篇 |
2007年 | 5365篇 |
2006年 | 4923篇 |
2005年 | 4079篇 |
2004年 | 3200篇 |
2003年 | 2932篇 |
2002年 | 3104篇 |
2001年 | 2705篇 |
2000年 | 1721篇 |
1999年 | 1269篇 |
1998年 | 880篇 |
1997年 | 699篇 |
1996年 | 560篇 |
1995年 | 415篇 |
1994年 | 349篇 |
1993年 | 243篇 |
1992年 | 161篇 |
1991年 | 148篇 |
1990年 | 121篇 |
1989年 | 96篇 |
1988年 | 68篇 |
1987年 | 65篇 |
1986年 | 42篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
为了提高E^2PROM中N管源漏穿通电压,用实验的方法对制造工艺进行了研究。结果表明,高能量注入是提高VPT的有效手段,但受到pn结击穿的限制,只适用于低区短沟N管;DDD工艺大幅度高VPT,但pn结击穿电压低于20V,不能应用于高压MOS管;采用适量的防穿通注入和适当增大沟道长度为最理想的工艺途径。 相似文献
32.
WJ Cho EK Kim MJ Park SU Choi CO Lee SH Cheon BG Choi BH Chung 《Canadian Metallurgical Quarterly》1998,6(12):2449-2458
In this study a series of 3-arylisoquinoline derivatives were synthesized and cytotoxicity against human melanoma tumor cell evaluated, and a three dimensional quantitative structure-activity relationship was investigated using the comparative molecular field analysis (CoMFA). The results suggested that the electrostatic, steric and hydrophobic factors of 3-arylisoquinolines were strongly correlated with the antitumor activity. Considerable predictive ability (cross-validated r2 as high as 0.721) was obtained through CoMFA. 相似文献
33.
新型高性能脉冲峰值保持电路 总被引:10,自引:7,他引:3
本文介绍了两种新型跨导型脉冲峰值保持器,分别用于多丝正比室(MWPC)和复合晶体闪烁探测器(Phoswich)输出脉冲信号的形状和幅度分析。电路的跨导放大级采用跨导型集成运算放大器,使电路结构简单化,且性能优良可靠,能响应输入脉冲最小上升时间分别为50ns(Phoswich)和500ns(MWPC)的信号,在40dB的动态范围内,两电路的积分非线性均好于0.1%,特别适用于空间γ射线观测。 相似文献
34.
介绍了给DY3000×20m数控机床大行程拖链增设的张紧装置,该装置解决了拖链无法自动复位的问题,使用方便、经济可行。 相似文献
35.
36.
联合站油水分离过程是将高含水原油处理成为合格产品的重要生产过程,从控制理论角度看,此过程具有多变量、干扰因素复杂、非线性、大滞后、压力与界面强耦合的特点,为了实现此过程的自动控制,本文针对典型的两段式脱水工艺进行了理论分析,通过对人工智能控制经验的总结,确定了模糊-PID控制策略。 相似文献
37.
Hyoung Jin Choi Yong Woo Inn Myung S. Jhon 《Korean Journal of Chemical Engineering》1994,11(3):145-152
Polymer migration is a generally well-known phenomenon in a flow field, and it has been verified that the sources of such
phenomena are nonhomogeneity of the flow, concentration effects and hydrodynamic interactions between the polymer molecules.
In addition, temperature effects were found to be another source of polymer migration. The Langevin equation for a polymer
molecule was first derived from single chain dynamics using a kinetic theory for the bead-spring elastic harmonic dumbbell
model, as described in part I (reference [1]). In this paper the diffusion equation and concentration profile of the polymer
molecules induced by a temperature gradient are obtained from the Fokker-Planck equation. A new differential operator is also
introduced to calculate the concentration profile. From the concentration equation obtained in the general flow geometry,
we find that in dilute polymer solution there are significant effects on the polymer migration not only due to the nonhomogeneity
of the flow field but also due to temperature gradients. 相似文献
38.
Won-Ho Lee Hyoun-Ee Kim Seong-Jai Cho 《Journal of the American Ceramic Society》1997,80(10):2737-2740
Microstructural evolution of gas-pressure-sintered Si3 N4 with Yb2 O3 as a sintering aid was observed. Microstructures typical for in situ toughened Si3 N4 , i.e., large elongated grains randomly distributed in a fine matrix, were observed. However, the size of the elongated grains near the surface was much larger than that at the center, resulting in two distinct regions: an inner region and an outer region. The smaller the amount of Yb2 O3 added, the larger the difference in the size of the elongated grains between the outer and inner regions. The difference between microstructures was diminished when 16 wt% Yb2 O3 was added. The microstructural change with Yb2 O3 content was attributed to the evaporation of Yb-containing liquid phase from the surface. 相似文献
39.
40.
The effects of estrogen-induced hyperlipidemia on plasma lipid peroxidation, fatty acid composition and osmotic fragility
of erythrocytes in chickens were studied. Young male chickens implanted with estrogen for three wk developed a marked hyperlipidemia.
Plasma levels of triglyceride, cholesterol and phospholipid were elevated 68-, four- and 24-fold, respectively, over controls.
There was also a two-fold increase in plasma lipid peroxidation measured by the thiobarbituric acid test. Vitamin E supplement
(1,000 IU/kg diet) reduced the plasma lipid peroxidation to the control level, but had no effect on the plasma lipid content.
Estrogen-induced hyperlipidemia resulted in changes in the fatty acid composition of membrane lipids of erythrocytes. The
major changes were an increase in oleic acid from 10.0% to 14.2% and a decrease in linoleic acid from 31.3% to 26.0%. The
erytrocytes with an altered membrane fatty acid composition were found to have an increased osmotic fragility. It was apparent
that there was a direct correlation between the oleic acid content and the osmotic fragility of erythrocytes. 相似文献